The present invention relates to a surgical suture anchor for implantation in solid tissue, such as bone, which is implantable without prior drilling of a hole in the solid tissue. More particularly, the present invention relates to a surgical anchor which can both pierce soft tissue, such as muscle, and drill into bone. The surgical anchor is self-setting within the solid tissue and serves as a point of attachment for suture material which serves to attach a soft tissue to the solid tissue containing the implanted anchor.
In orthopedic surgery there is often a need to attach a soft tissue, including but not limited to muscle, to a solid tissue, including but not limited to bone. A number of prior art devices, referred to collectively as suture anchors, exist to perform this function.
Suture anchors for anchoring a suture to solid tissue, such as bone, so that a soft tissue, such as muscle or ligament, may be sutured to the bone are known in the art. Such suture anchors come in a variety of shapes and designs which are reviewed in James E. Carpenter et al., "Pull-Out Strength of Five Suture Anchors", Arthroscopy, 9(1), pp. 109-113 (1993). These suture anchors may be divided into several categories.
The first category is the harpoon-type or screw-type suture anchor, which are drilled into cortical bone. This type is represented by, for example, Cerrier et al. U.S. Pat. No: 5,100,417 and Hayhurst et al. Canada PAT. NO: 2,045,903. This type of suture anchor is held in place by a variety of methods including self-tapping, force fitting, and inclusion of a resilient portion which flexes to frictionally engage the bone material.
An additional category of suture anchor includes a rigid member and a flexible, shape memory member. The flexible member lies flat against the rigid member during insertion, and flexes away from the rigid member once lodged inside the bone. This category includes, for example, the prior art teachings of Gatturna et al. U.S. Pat. Nos: 5,046,513 and 5,192,303.
A third category of suture anchor is substantially elongated and is inserted with its longitudinal axis substantially parallel to the bone hole through which it is inserted. The orientation of the suture anchor is then adjusted upon reaching cancellous bone tissue by pulling on the attached suture. This category of anchor is exemplified by Hayhurst et al. U.S. Pat. No: 5,041,129 and Noblitt et al. U.S. Pat. No: 5,203,787.
According to the teachings of Hayhurst, the suture anchor has a substantially cylindrical rigid body with a central cavity and a longitudinal slot extending from one end to approximately the middle of the rigid body. A suture is positioned inside the central cavity, and the anchor is inserted with the slot entering the bone last. After properly positioning the anchor, the suture is pulled through the slot towards its base, thereby reorienting the anchor with respect to the bone, thereby fixing it in place.
According to the teachings of Noblitt, the suture anchor has an offset portion to facilitate attachment of a suture. Once the anchor has been placed in cancellous tissue, the suture is pulled in such a way that it reorients the anchor so that its longitudinal axis is substantially transverse to the bone hole through which it was inserted.
A disadvantage common to all members of this third category of anchors is that tension on the suture required for reorientation of the anchor may put undue stress on the suture. In addition, the introduction technique is complicated, requiring multiple insertion tools.
All of the above-described suture anchors typically require complex insertion tools, the use of which is time consuming and requires considerable skill. Insertion of these prior art devices often requires pre-drilling of the bone (U.S. Pat. Nos.: 4,898,156; 4,899,743; 4,946,468; 4,968,315; 5,002,550; 5,501,695; 5,540,718). Pre-drilling is disadvantageous because it requires positioning of a soft tissue relative to a solid tissue, selection of a site for drilling, release of the soft tissue, drilling into the solid tissue, insertion of the anchor, and repositioning of the soft tissue. This process is time consuming and difficult. Repositioning of the soft tissue after drilling may be inexact, leading to sub-optimal attachment. The process lengthens the time of surgery increasing patient anxiety and distress.
A fourth category of anchors includes screws which are either self-tapping (for example U.S. Pat. No: 4,632,100) or require drilling of a pilot hole. Screws often loosen with time, necessitating a second operation to remove the loosened screw. In addition, when screws are set in bone, the heads of the screws can protrude above the surface of the bone in which they are set. These exposed screw heads present an abrasive surface to surrounding soft tissue which may cause inflammation or tissue damage. If a pilot hole must be drilled into the bone, the installation procedure becomes lengthy, more so if the pilot hole must be tapped to accept the screw. In addition, the nature of a screw attachment tends to require that the pilot hole be located on a relatively flat section of the bone, and toothed washers must frequently be used in conjunction with the screws to fasten the desired objects to the target bone. As a result of these constraints, it may be necessary to locate the attachment point at a less than optimal position.
A fifth category of anchors includes staples which are tapped or hammered into the bone. Staples have their own set of disadvantages. Bone staples must frequently be removed after they have been in position for some time, necessitating a second operation. In addition, staples must be positioned so as to maximize their holding power in the bone and such positioning may conflict with the otherwise-optimal position for attachment of objects to bone. The most serious drawback of staples is that they may crack the bone during deployment, or accidentally transect the object (e.g. soft tissue) being attached to the bone, since it is difficult to control the extent of the staple's penetration into the bone. Finally, once the staple has been set into the bone, it is impossible to adjust the degree of tension being applied to the object which is being attached to the bone without setting a new staple.
In addition, prior art anchors which require drilling of holes in the bone typically require holes with a diameter between 2.4 and 3.7 mm (radius (r) of 1.2 to 1.85 mm). Since weakening of the bone is proportional to the area of the hole drilled, and since the area (a) increases according to the formula a=.pi.(r.sup.2) a small reduction in the diameter of the hole will greatly reduce the area of the hole and therefore greatly reduce the degree to which the structural integrity of the bone is compromised. For example, a prior art device requiring a hole with a diameter of 2.4 mm has an area of 4.52 mm.sup.2. Reducing the diameter of the hole to 1.8 mm, a 25% reduction, reduces the area to 2.54 mm.sup.2, a reduction of 44%. Therefore, any invention which reduces the size of the hole in the bone required to implant an anchor is inherently advantageous because it facilitates retention of more of the structural integrity of the bone.
The prior art teaches coating of materials to be implanted within the body with bio-resorbable polymers such as poly (alpha-hydroxy-carboxylic acid)/poly (oxyalkylene) to reduce inflammation and adhesions after surgical implantation of a foreign body within a patient. (for example U.S. Pat. Nos: 4,826,945 and 5,711,958). This material, or other bio-resorbable polymers, may be used in conjunction with implantable surgical anchors.
Citation or identification of any reference in this section or in any other section of this application shall not be construed as an admission that such reference is available as prior art to the present invention.
There is thus a widely recognized need for, and it would be highly advantageous to have, a surgical suture anchor which does not require pre drilling of a hole, which is unthreaded, which can be installed without benefit of special tools, which concurrently pierces soft tissue and bone, and which makes a narrower diameter hole in the bone than existing alternatives.